The invention relates to a process for finishing the edge of corrective lenses made of plastic and in particular of corrective lenses made of thermoplastic or of a mixture of a thermoplastic and a thermosetting plastic.
A corrective lens edge grinding machine suitable for such a process is described in German utility patent specification, patent number 86 23 058. This patent discloses a set of grinding wheels which differ from one another, for the preliminary and finishing steps of grinding corrective lenses on a carrier frame which is mounted slidingly in two horizontal coordinate axes on the base frame and which carries the grinding wheel with a drive motor.
As a rule, a corrective lens will be pre-profiled while still wet with the assistance of a template, by means of a roughing wheel, whereby the greatest part of the glass to be removed is removed during this phase. This is followed by wet post-profiling including, if appropriate, simultaneous grinding of the peripheral bevel, and calibrating at a further cylindrical wheel exhibiting a grain of appropriate fineness.
In this prior known process for finishing corrective lens edges, it is difficult to achieve sufficient surface quality at the edges of the corrective lens during post-profiling and calibrating. Particularly in the case of rimless spectacles, a great emphasis is placed on achieving a smooth, finely finished glass edge. Furthermore, when finishing the edges of ophthalmic lenses made of plastic, and in particular, those made of thermoplastic materials, there is a danger that this material will be heated during the grinding step, and that the abraded material will load up on the fine-grained surface of the post-grinding wheels, causing them to clog.